A crystalline lens gets colored in yellow as people get old, and the color becomes denser. When the crystalline lens so-colored in yellow is removed, no filter effect works, and there appears a phenomenon that objects look bluish. This phenomenon is called Ocyanopsian, and it is a cyanopsia-correcting intraocular lens colored in yellow that corrects the above phenomenon to bring the vision close to the normal vision. As the above cyanopsia-correcting intraocular lens, there has been used a hard lens made of polymethyl methacrylate (PMMA).
In recent years, there has been developed a small incision operating method which aims at a simple operation, a decrease in the occurrence of astigmatism after the operation and sooner recovery therefrom. A soft intraocular lens attracts attention as a lens for the above small incision operation, which soft intraocular lens is made of a silicone or acrylic material and can be inserted through a small incision in a folded state. However, no soft intraocular lens which works to correct cyanopsia has been commercially available. The reason therefor is that when a soluble or dispersible colorant for the above hard lens made of PMMA is used in a soft material, there is caused a big problem that the colorant bleeds out. The bleeding-out is a phenomenon that the internal molecular chain of a soft material undergoes intense motion due to a low glass transition temperature of the soft material so that a dissolved or dispersed colorant migrates onto a lens surface.
For overcoming the above problem, for example, there has been proposed a soft intraocular lens, in which an ultraviolet absorbent and a yellow dye are decreased in amount for controlling the elution of these (JP-A-7-24052). However, the above soft intraocular lens is not yet satisfactory.
As an ultraviolet absorbent, there is known a compound having a monomer structure which permits copolymerization with a monomer for a lens. For example, there is disclosed a reactive ultraviolet absorbent having a benzotriazole structure and having excellent copolymerizability and hydrolysis resistance (JP-A-8-311045). Further, as a reactive yellow dye, there has been disclosed an azobenzene-based yellow dye (Japanese PCT Publication No. 8-503997). The use of the above ultraviolet absorbent or yellow dye having a monomer structure is indispensable to ophthalmic lenses such as a hydrous contact lens and an oxygen-permeable hard contact lens, particularly to a soft intraocular lens.
As a reactive ultraviolet absorbent, a variety of compounds have been developed from the viewpoint of absorption spectrum, solubility, reactivity and durability. However, as a reactive yellow dye, few compounds have been developed, or no satisfactory compound is available.
For example, a compound of the formula (II) is known as a reactive yellow dye (JP-A-10-195324). ##STR1##
The above compound is satisfactory in view of solubility in various monomers for lenses and copolymerizability therewith. However, the above compound has problems that it has a maximum absorption of spectrum in approximately 350 to 360 nm and that its molecular extinction coefficient is relatively small. That is, the above compound is insufficient in absorption of light in a region of from 400 nm to 500 nm, which absorption is considered effective for correcting cyanopsia. Another problem is that the amount of the above compound to be used is relatively large when it is used.
In view of safety and the filter effect, there has been desired a reactive dye which exhibits a sufficient filter effect when a low concentration of it is added. This point is very important for a contact lens which is to come in contact with corneal mucosa and an intraocular lens which is to be implanted in an eye.
Under the circumstances, it is an object of the present invention to provide a novel compound which is excellent in solubility in a monomer for a lens and copolymerizability with the monomer, which undergoes no elution during extraction with various solvents, which has an excellent absorption peak in a visible light region when used in an ophthalmic plastic lens and which works sufficiently in a small amount.
It is another object of the present invention to provide an ophthalmic plastic lens, particularly an intraocular lens such as a soft intraocular lens, to which the above novel compound is applied.
Further, it is another object of the present invention to provide a process for efficiently producing the above ophthalmic plastic lens.